The clinical problem: Breast cancer is the commonest cancer in women, in whom it is second only to lung cancer as a cause of cancer death. Mammography is the mainstay of screening for breast cancer, though its value is limited by its large number of false-positive and false-negative findings. A new solution the problem: The combination of two diagnostic tests with different biological mechanisms can be more sensitive and specific than either test employed alone. The BreathLInk breath test for biomarkers of breast cancer could potentially increase the sensitivity and specificity of mammography, and significantly reduce the number of false-positive and false-negative test results arising from mammography. Goal of the research: We will test the hypothesis that the BreathLink breath test combined with mammography will result in significantly fewer false-positive and false-negative test results than with mammography alone. We will achieve this goal by performing BreathLink breath tests in 2,000 women at five sites who are having mammography for breast-related symptoms or signs (e.g. breast mass). Expected outcomes of the research: We expect that that the BreathLink breath test combined with mammography will significantly reduce the number of false-positive and false-negative test results arising from mammography alone. This research could establish a new paradigm for detecting women with breast cancer. The combination of an intrinsically safe breath test with mammography could potentially reduce the number of needless mammograms and breast biopsies that are now performed, with a commensurate reduction in radiation exposure, discomfort, complications of biopsies, and costs to the health care system.